Multiwavelength generation lasers have been increasingly demonstrated over the past several years. For example, the subject invention assignee as been at the forefront of developing multiwavelength modelocked semiconductor diode lasers. See for example, Shi et al. xe2x80x9cFour-wavelength, 10-GHZ picosecond pulse generation from an active modelocked single-stripe diode laser,xe2x80x9d Conference proceeding presentation on May 18-23, 1997, OSA Technical Technical Digest Series Vol. 11, Conference on Lasers and Electro-optics (CLEO), 1997; and Mielke et al. xe2x80x9c60 channel WDM transmitter using multiwavelength modelocked semiconductor laser,xe2x80x9d Electron. Lett., v 38 n 8 Apr. 11, 2002. P. 368-370. Wavelength division multiplexing (WDM) in telecommunication and data transmission systems increases system capacity by more fully taking advantage of the intrinsic bandwidth of installed optical fiber. Channel widths and spacings have been standardized so those necessary system components such as lasers and spectrally dispersive components can be designed for interoperability. Simultaneously, the data rate of individual channels is being pushed toward higher rates with approximately 10 Gbit standards (both Sonet and Ethernet) near deployment. Current architectures utilize a separate laser for each wavelength channel introducing complexity and cost issues. Significant research has been conducted to develop and assess potential multiwavelength sources for WDM systems. Multiple active device arrays of both laser diodes and vertical cavity surface emitting lasers (VCSELs) have been constructed and tested but problems with growth control toward exact spectral emission remain a concern. See Kudo, K., Furushima, Y., Nakazaki, T., Yamaguchi, M., xe2x80x9cMultiwavelength microarray semiconductor lasersxe2x80x9d, Electron. Lett., v 34 n 21 Oct. 15, 1998. P. 2037-2038. Continuum generation in optical fibers from high power pulsed sources followed by spectral filtering has been demonstrated but suffers from the need for the high power front end as well as the power inefficiency of discarding much of the generated spectrum in the filtering process. See Morioka, T., Mori, K., Kawanishi, S., Saruwatari, M., xe2x80x9cMulti-WDM-channel, Gbit/s pulse generation from a single laser source utilizing LD-pumped super continuum in optical fibersxe2x80x9d, IEEE Photonics Tech. Lett., v 6 n 3 March 1994. P. 365-368.
Multiple-quantum-well devices with individually shifted spectral gain have also been constructed and utilized downstream spectral filtering with the attendant power inefficiencies. See Coudenys, G., Moerman, I., Zhu, Y., Van Daele, P., Demeester, P., xe2x80x9cMultiwavelength InGaAs/InGaAsP strained-layer MQW-laser array using shadow-masked growthxe2x80x9d, IEEE Photonics Tech. Lett., v 4 n 6 June 1992, p 524-526. Cavities based on various grating technologies, Zhu, B., White, I., xe2x80x9cMultiwavelength picosecond optical pulse generation using an actively modelocked multichannel grating cavity laserxe2x80x9d, Journal of Lightwave Tech., v 13 n 12 December 1995, p 2327-2335, and erbium fiber ring cavities with distributed fiber gratings or etalons have also been demonstrated. See Papakyriakopoulos, T., Stavdas, A., Protonotarios, E., Avramopoulos, H., xe2x80x9c10xc3x9710 GHz simultaneously modelocked multiwavelength fibre ring laserxe2x80x9d, Electron. Lett., v 35 n 9 Apr. 29, 1999 p 717-718 and Chow, J., Town, G., Eggleton, B., Ibsen, M., Sugden, K., Bennion, I., xe2x80x9cMultiwavelength generation in an erbium-doped fiber laser using in-fiber comb filtersxe2x80x9d, IEEE Photonics Tech. Lett., v 8 n 1 January 1996, p 60-62.
A common problem with current multiwavelength generation systems is that the individual channels often generate pulses having different amplitude (intensity) values. A further problem with current multiwavelength generation systems is the lack of control over the interwavelength phase coherence properties.
In addition to the subject assignee""s contributions, over the years various attempts have been made for generating multiwavelength lasers. See for example, U.S. patents: U.S. Pat. No. 6,018,536 to Alphonse; U.S. Pat. No. 6,061,369 to Conradi; U.S. Pat. No. 6,064,681 to Ackerman; U.S. Pat. No. 6,192,058 to Abeles; U.S. Pat. No. 6,275,511 to Pan et al. However, none of the known prior art overcomes the problems of consistently and actively preventing uneven amplitude values for each of the multiwavelength channels nor does it offer flexibility and command of the phase coherence properties of the emitted light.
A primary objective of the subject invention is to provide a multiwavelength laser method and system that reduces undesirable intensity fluctuations on individual wavelength channels.
A secondary objective of the subject invention is to provide a multiwavelength laser method and system that provides an xe2x80x9cerror-freexe2x80x9d pulse train simultaneously into each of its discrete wavelength channels.
A third objective of the subject invention is to provide a multiwavelength laser method and system that reduces amplitude noise in multiwavelength modelocked semiconductor lasers.
A fourth objective of the subject invention is to provide a multiwavelength laser method and system with better longitudinal mode phase coherence properties.
A fifth objective of the subject invention is to provide a multiwavelength laser method and system with specific tailored interwavelength phase coherence properties, including a high coherence operational mode as well as a low coherence operational mode.
A sixth objective of the subject invention is to provide a multiwavelength laser method and system that generates a large plurality of wavelength channels (up to and greater than 100 channels) by combining gain flattening and noise suppression.
Multiwavelength modelocked optical laser systems and methods. The preferred embodiments of the system and method can include lens, semiconductor optical amplifier, grating, cylindrical lens, rod lens and an approximately 7 nm MQW saturable absorber between mirrors for providing a laser cavity resonator for hybridly modelocked operation.
Two preferred embodiments illustrate two different positions for the saturable absorber inside the laser resonator which enables direction of the interwavelength phase coherence properties. The invention has been demonstrated to generate up to approximately 300 MHz optical pulse trains in each of up to approximately three channels.
An additional embodiment can include combining gain flattening and noise suppression within the optical cavity of the modelocked laser that can result in generating up to approximately 123 wavelength channels, each having up to approximately 6 Giga Hertz optical pulse trains.
Further objectives and advantages of this invention will be apparent from the following detailed description of presently preferred embodiments which are illustrated schematically in the accompanying drawings.